Conservative groups have filed a lawsuit attempting to prevent a citizen initiative that targets anonymous campaign spending in elections from appearing on the Arizona ballot.

The lawsuit, filed Thursday, aims to disqualify thousands of signatures collected in support of the "Outlaw Dirty Money" constitutional amendment, which would make public the identity of all major campaign contributors.

The campaign's supporters need 225,963 valid signatures for their amendment to remain on the Nov. 6 ballot. They submitted 285,768 signatures.

The lawsuit doesn't specify how many signatures opponents believe are invalid. But it states numerous petition sheets must be disqualified because they were collected by paid gatherers who aren't registered with the state, as the law requires, or who are convicted felons.

In Arizona, citizen groups that bring initiatives to change state law must comply with a strict set of rules, including a requirement that any paid petition gatherers be eligible to register to vote.

The lawsuit alleges that some petition gatherers for the Outlaw Dirty Money amendment are felons who haven't had their civil rights restored.

Campaign: Billionaire Koch brothers connected to lawsuit

Plaintiffs in the lawsuit include the leaders of high-profile conservative political organizations known as "dark money" groups because they spend heavily to influence elections without disclosing their donors.

They include Andrew Clark, state director for Americans for Prosperity, a group with deep ties to billionaire brothers David and Charles Koch; and Scot Mussi, director of the Arizona Free Enterprise Club.

The Outlaw Dirty Money campaign responded to the lawsuit by blasting the Kochs, asserting they want to hide their political influence in Arizona. The campaign extended a "standing invitation" to the brothers to debate the issue of anonymous spending in elections.

"It’s unfortunate that neither of the Koch Bros. is willing to come out of hiding, get here to Arizona, and debate why their dirty money is good for our state," the campaign said in a statement.

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"In the meantime, the Outlaw Dirty Money committee has been prepared for them and this tactic for months. Arizona citizens deserve the right to vote on this issue and we are determined to protect that right.”

An attorney for the plaintiffs in the lawsuit didn't immediately respond to a request for comment. Media representatives for Koch Industries, Inc., didn't respond to a request for comment.

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Anonymous interests spent at least $15 million trying to get their favored candidates installed in Arizona’s state and legislative offices in 2014. A look at the “dark money” major players, the spoils by state office, plus the top 10 lawmakers to benefit from - but not directly coordinate with those who spent - anonymous cash: Getty Images/iStockphoto

DARK MONEY PLAYERS. Arizona Free Enterprise Club spent $1.73 million in 2014 to try to get its candidates elected, followed by the 60 Plus Association ($1.69 million) and American Encore ($1.46 million). All three groups have ties to the Koch network. Photo by Getty Images/iStockphoto

GOVERNOR. $5.2 million. Republican Doug Ducey won with help from his secret friends, including the Arizona Free Enterprise Club and American Encore, groups that have ties to billionaires Charles and David Koch. Photo by Mark Henle/The Republic

CORPORATION COMMISSION. $3.2 million. Republicans Doug Little and Tom Forese got a boost from the Arizona Free Enterprise Club and Save Our Future Now, which were likely bankrolled by APS, a utility with business before the commission. Photo by Cheryl Evans/The Republic

EDUCATION SUPERINTENDENT: $394,000. David Garcia, a Democrat, lost his bid for the seat despite the efforts of Stand for Children Inc., funded in part by former New York Mayor Michael Bloomberg. Photo by Michael Schennum / The Republic

SEN. BOB WORSLEY: $120,000. Worsley, R-Mesa, enjoyed help from the Arizona Business Coalition, Stand for Children and Arizonaw 2014 to successfully fend off a serious primary challenge bankrolled by $42,000 in dark money. Photo by Michael Chow/The Republic

SEN. SYLVIA ALLEN. $73,000. Allen, R-Snowflake, was aided by the Arizona Free Enterprise Club, the American Federation for Children and the Center for Arizona Policy Action. Photo by Rob Schumacher/The Republic

REP. DOUG COLEMAN. $44,000. Coleman, R-Apache Junction, was aided by the dark-money Arizona Business Coalition, Stand for Children and the American Federation for Children. This, to combat a $54,000 dark-money campaign to bounce him out of office. handout photo

SEN. CARLYLE BEGAY. $44,000. Begay, then-D-Ganado, enjoyed help from Friends of Arizona and the American Federation for Children to defeat three candidates who got no dark money support. Begay has since become a Republican. Photo courtesy Carlyle Begay

REP. BOB ROBSON. $43,000. Robson, R-Chandler, was backed by the Arizona Business Coalition, Stand for Children and the Arizona Residents Council. Arizona Free Enterprise Club plunked down more than $40,000 to defeat him. handout photo

REP. JILL NORGAARD. $37,000. Norgaard, R-Phoenix, benefitted from the efforts of the Arizona Free Enterprise Club and American Federation for Children. Her GOP opponent, John King, got $22,000 in dark money support. Photo by Todd Johnson

Interested in this topic? You may also want to view these photo galleries:

Amendment targets secret campaign spending

The proposed amendment, if passed by voters, could have a drastic impact on millions of dollars spent to influence elections in Arizona.

It would require anyone spending more than $10,000 to oppose or support candidates or ballot measures to disclose everyone who contributed $2,500 or more to the effort. Violators would be subject to fines.

The initiative's main proponent is Terry Goddard, a Democrat who formerly served as Arizona's attorney general. But the effort has bipartisan support, including the backing of Tom Horne, a Republican and another former attorney general.

State election officials are vetting signatures the proponents submitted to place the amendment on the ballot. That review is expected to be completed by late August.